Actuating device of this class are used, for example, but by no means exclusively, for manually selecting gears or for gear preselection in speed-change gears of motor vehicles.
The gear is preselected or the operating state of the vehicle transmission is controlled now in an increasing number of motor vehicle models by means of electrical or electronic signal transmission. An electrical or electronic actuation of technical systems or transmissions, which makes do without mechanical connection in this manner, does, however, entail that the operator or the driver has, in general, no feedback whatsoever on the execution of a control command and optionally also no feedback on the fact that his actuating command may not be admissible, contrary to operation by means of the prior-art mechanical actuating device.
It may rather happen in actuating device with push buttons and with electrical or electronic signal transmission that the system or vehicle transmission to be controlled does not assume the operating state associated with the pressed push button for certain reasons after one of the push buttons of the actuating device has been pressed. In other words, this means that the desired state of the controlled system, for example, of the vehicle transmission, which state is selected by pressing the push button, does not agree with the actual shifting state of the system or transmission. Such a divergence between the actual operating state of a technical system and the control command—presumably—entered with the controlling push buttons may have various causes.
In the case of the example of the control or gear preselection on an automatic transmission of a vehicle, motor vehicles equipped with automatic transmission are frequently provided with a so-called shiftlock function. Especially the shift positions “D” and “R” can be selected from the neutral position “N” in a vehicle with shiftlock function only when the brake pedal is pressed at the same time. This is used for safety and shall prevent a gear from being engaged with the engine running, for example, by inadvertently striking the gear selector lever of the transmission and the vehicle from coming into motion in an uncontrolled manner.
However, in case of an electrical or electronic push button control of a shift-by-wire vehicle transmission, which is provided with a shiftlock function, the driver could select, for example, the shift position “D” by pressing the corresponding push button when the brake pedal is not pressed. However, since the brake pedal is not pressed in the case of the example, the transmission remains in the neutral position “N” without any change because of the shiftlock function, whereas the driver believes after pressing the push button “D” that the corresponding gear is now engaged.
As a result, this situation leads to a potential safety risk, because the vehicle may inadvertently roll backwards on a slope in such a case, or the driver may not leave a hazardous situation quickly enough in the false belief of having engaged the Drive gear.
Furthermore, there also may be, for example, a malfunctioning or non-functioning transmission of the control commands between the actuating device and the system or vehicle transmission controlled therewith, with the consequence that the gear preselected by the driver on the actuating device is not recognized by the system and the corresponding control command is thus not sent to the transmission.
A hazardous situation of this type is given in case of the push button-controlled actuation of a motor vehicle transmission, for example, when the driver brings the vehicle to a stop after driving with the gear “D” engaged and selects the shift position “P” for the parking brake with the engine running. However, the Drive gear “D” continues to be engaged if the signal transmission is not functioning between the actuating device and the vehicle transmission, without the non-functioning signal transmission being communicated to the driver during his attempt at engaging the parking brake. If the driver now leaves the vehicle in the belief that he has engaged the parking brake, the vehicle will set automatically into motion because the gear is actually still being engaged.